1. Field of the Invention
The present invention relates to electrodepositable coating compositions containing flatting agents and their use in electrodeposition.
2. Brief Description of the Prior Art
Electrodepositable coating compositions, such as, electrodepositable primers typically contain flatting agents to reduce the gloss and impart a dull finish to the cured coating film. Traditionally, these flatting agents have been inorganic pigments and fillers, such as silicas, clays or talcs. Although these materials are effective for this use and relatively inexpensive, they tend to settle out readily and adversely affect final film properties. Clay and talc, in particular, contain various partially soluble contaminants, such as iron, which reduce the corrosion resistance of the electrodepositable coating. In addition, these inorganic materials can have other deleterious effects. For example, clay can detract from the flexibility of the cured film while certain silicas can be toxicologically undesirable.
Flatting agents made from organic materials are well known in the art. Typical organic compounds which are employed are acrylic and polyester polymers. The disadvantage of the polymeric acrylic flatting agents is their high cost relative to polymeric polyesters. Crosslinked polyesters, such as those described in U.S. Pat. Nos. 3,879,314, 3,923,704 and 4,483,945 are well known as matting agents for latex paints. These crosslinked polyesters are suspensions of polymeric particles in an aqueous medium, prepared by suspension polymerization techniques, and as such are highly susceptible to settling, agglomeration or kickout. Moreover, the polymeric particles as prepared are often of dimensions which hamper formulation into coatings or cause filtration problems during paint production, such as filter plugging. In addition, milling of the particles to reduce size can be difficult due to the nature of the particle. Such organic flatting agents have not been used in electrodepositable coating compositions heretofore.
It would therefore be desirable to have an organic flatting agent such as the crosslinked polyesters that overcomes the particle size and stability drawbacks mentioned above, which when incorporated into electrodepositable coating compositions provides flatting comparable to conventional inorganic pigments without compromising film properties such as corrosion resistance and flexibility.